The present invention relates to a feedback or echo cancellation assembly and methodology that may be utilized to improve feedback cancellation performance in a wide range of electroacoustic communication apparatuses. The feedback or echo cancellation assembly may be utilized in portable communication devices such as smartphones, laptops, tablets and other types of audio enabled portable computing devices. The feedback or echo cancellation assembly may also be integrated in an electroacoustic communication apparatus of a motorized vehicle such as a car, i.e. an automotive application. In the latter case, the electroacoustic communication apparatus may form part of an in-car music entertainment and communication system with build-in hands-free speaker functionality. The feedback or echo cancellation assembly suppresses acoustic coupling via an external feedback path between a loudspeaker and a microphone of the electroacoustic communication apparatus by determining and adding an opposite phase feedback cancellation signal to a summing node of a signal reception path of the electroacoustic communication apparatus.
In prior art feedback or echo cancellation systems and methodologies, the feedback cancellation signal has typically been generated by a linear adaptive digital filter of an electronic feedback cancellation path. The linear adaptive digital filter models or tracks stationary and constant or time-varying frequency response characteristics of the external acoustic feedback path and produces the opposite phase feedback cancellation signal. While a suitably configured linear adaptive digital filter may be capable of accurately modelling characteristic of the external acoustic feedback path itself because the latter normally behave essentially linearly, the linear adaptive digital filter is unable to accurately model electrical, acoustic or electroacoustic components of the feedback or echo cancellation assembly of the electroacoustic communication apparatus that behave non-linearly within the desired operational range of signals. The lacking ability to accurately model the electrical, acoustic and electroacoustic components of the electroacoustic communication apparatus leads to an inaccurate feedback cancellation signal therefore deteriorating performance of the feedback cancellation assembly. The deteriorating the feedback cancellation performance may lead to various undesirable sonic artifacts of the reproduced sound such as echoes or instability in the electroacoustic communication apparatus.
Hence, there is a need for an improved feedback or echo cancellation assembly and methodology that are capable of accurately modelling non-linear behaviour of electrical, acoustic and electroacoustic components of a feedback cancellation assembly of electroacoustic communication apparatuses. An improved feedback or echo cancellation assembly capable of modelling at least a dominant non-linear component of the feedback or echo cancellation assembly, such as a loudspeaker, would be particularly advantageous. Loudspeakers, in particular electrodynamic loudspeakers, are generally highly non-linear devices at high sound pressure levels even within their nominal sound pressure output range. Hence, the loudspeaker will therefore often constitute the dominant non-linear component of the feedback or echo cancellation assembly.
The present invention provides an improved feedback or echo cancellation assembly by virtue of an electronic feedback cancellation path which comprises a non-linear digital loudspeaker model capable of accurately modelling the non-linear behaviour of the loudspeaker leading to significant improvement of the feedback cancellation performance. The non-linear digital loudspeaker model comprises at least one non-linear loudspeaker parameter derived from a voice coil current and/or a voice coil voltage of the loudspeaker. The at least one non-linear loudspeaker parameter is represented by a non-linear function between the at least one non-linear loudspeaker parameter for example a B*I product and a predetermined loudspeaker variable such as diaphragm excursion. The skilled person will understand that the non-linear digital loudspeaker model may comprise several non-linear loudspeaker parameters, represented by respective non-linear functions, to improve its accuracy to any desired performance level.
It is furthermore advantageous to provide a non-linear digital loudspeaker model that can be calibrated without requiring time-consuming and costly individual characterization of the behaviour of the non-linear loudspeaker parameter or parameters of each individual loudspeaker during manufacturing of the present feedback or echo cancellation assembly. It is also desirable to minimize the amount of computational resource expenditure of a digital signal processor implementing the non-linear function or functions of the non-linear digital loudspeaker model.